We previously reported the specific in vivo uptake and retrograde transport of antibody to dopamine-beta-hydroxylase (AD beta H) by noradrenergic (NA) neurons in the rat brain. The objective of the present study was to further explore this preliminary observation: (1) To examine the process by which AD beta H is taken up into NA neurons and (2) to utilize this unique uptake and retrograde flow phenomenon to elucidate the circuitry and origin of NA innervations to specific brain regions. Pharmacological destruction of adrenergic neurons by 6-hydroxydopamine blocked the uptake of AD beta H; further evidence that this immunoglobulin is taken up exclusively into dopamine-beta-hydroxylase (D beta H) containing neurons. Pharmacological manipulations with adrenergic agents suggest that the AD beta H uptake process is related to the norepinephrine (NE) release mechanism. Minute volumes of AD beta H were stereotaxically injected into 41 sites within the spinal cord, brainstem, diencephalon and telencephalon of anesthetized rats. Utilizing the specific AD beta H uptake and retrograde flow characteristic of NE neurons, it was possible to elucidate the specific NE circuitry to each of these areas and the associated pathways. This neuroanatomical technique is presently the most sensitive technique for the detection and elucidation of CNS NE circuitry.